Study On Gas Occurrence Characteristics And Desorption Law And Application In Deep Coal Seam

This paper studied gas occurrence characteristics in deep coal seam with highstress,high temperature and high pore pressure field and coal gas desorption laws indifferent medium, and put forward a new coal seam gas content measurement methodduring geological exploration based on coal gas desorption laws research results,andlaid the foundation. to further reveal gas occurrence mechanism in deep coal seam.Firstly, on the basis of previous research results, coal reservoir characteristics,gasoccurrence state, migration process and their influence factors in coal seam wereanalyzed in detail. Deep coal seam pore and adsorption were tested in the laboratory,andconclusion from the experiment was that gas adsorption capacity of the same coal seamis enhanced with increase of depth under the same experimental conditions,and thatsome coal isothermal adsorption curves aren’t not consistent with the Langmuirequation.After that, based on seepage theory and multi-physical coupling theory, fluiddynamic field coupling model of gas occurrence in deep coal seam was established forthe first time,and mathematical model was solved by using numerical analysissoftware--Comsol Multiphysics. The analysis results show that gas pressure and burieddepth is approximate linear relationship,and that coal seam gas content and deepness isapparent nonlinear relation, gradient decreases when reaching a certain depth;and Coalporosity and permeability decreases with the increase of depth.Comprehensive analysis results of laboratory test, numerical simulation and fieldstatistical show that micropore and gas pressure in deep coal seam increase, accordinglygas adsorption capacity is also enhanced,but gas content increased gradient willdecrease due to obvious influence of temperature, finally will no longer increase.A equipment for simulating coal seam gas desorption was developed throughcomparison of different schemes, it had four functions and realized separation of slurrypressure gas (N2) and desorption gas (CH4),which provided experimental base toresearch coal gas desorption laws in different medium. Based on Fick’s law of diffusionand simulation testing device, coal gas desorption laws in air and slurry medium weresystemly studied.,research result showed that curve fitting effect of power function classis superior to exponential function class about gas desorption process in the air; Coal gas desorption curve in slurry medium under non-pressure conditions formed anelongated "S" shape，it is completely different from desorption characteristics in the airmedium.So coal core gas loss quantity during drilling coring can not be accuratelypredicted if we use coal gas desorption laws in air medium.Finally,based on causes of error about geological exploration drilling desorptionmethod and coal gas desorption laws research results, new gas loss compensationmethod (simulation approximation) and gas residue quantity measurement technologywere put forward, and they achieved better results by practical application.